The evolution of a plane mixing layer with spanwise nonuniform forcing

The experimental studies of Nygaard and Glezer (AIAA Paper No. AIAA‐91‐0625, 1991) show that vortical structures shaped like a ‘‘chain‐link fence’’ form in a plane mixing layer subjected to spanwise nonuniform phase excitation. Using direct numerical simulation of temporally evolving mixing layers, initial conditions have been developed that result in flows with vortex structures similar to those observed in the experiments. The simplest initial condition that leads to the experimentally observed structures is composed of a pair of equal‐strength oblique disturbances and this initial condition is a low‐order Fourier approximation to the square‐wave excitation used in the experiments. This simple disturbance suggests an explanation for the short wavelength cutoff observed in the experiments and allows comparison with previous stability analyses. The simulated flow fields show that the chain‐link‐fence vortex structures are different from the usual rib/roller mixing layer structures. Furthermore, detailed e...